Moisture sensitive materials, such as pharmaceutical products, are often stored and shipped in water-proof resealable containers. When these containers are opened in order to access the products, the air that is present inside the container and outside of the container mix which often results in a change in the relative humidity of the air within the container. The container and its cap may also be permeable to air over extended periods of time. In addition, there may be changes in the relative humidity level within the container, if there is a leak in the container.
These changes in the relative humidity level within a container may adversely affect the products which are stored within the container. It is often important to maintain an essentially constant relative humidity level within the container or within larger shipping packages holding multiple containers or even in storage rooms for the containers.
To prevent excessively high relative humidity levels from adversely affecting products, manufacturers commonly place desiccants within a container or with shipping packages for multiple containers to adsorb excess moisture from the air that enters the container. Conventional desiccants include silica gel, clay, molecular sieves, etc. Desiccants used in this manner reduce the level of moisture within the container to a relatively low level, based on the moisture absorption capability of the desiccant that is chosen.
However, in order to avoid deterioration of the stored goods, it is in many cases necessary to maintain a relative humidity within the container that is higher than would be achieved from the use of conventional desiccants in a “dry” state i.e. in a state in which essentially no water has been adsorbed.
This has been especially important for products which retain significant quantities of moisture, such as vegetables, flowers or tobacco products. Thus, humectant materials have been used to maintain a predetermined hydration level within a container. For instance, moistened pads have been used to assist in the maintenance of high humidity within such containers.
The disadvantage related to such moistened pads is that they readily act as humectants, i.e. moisture is readily desorbed or vaporized, but moisture is scarcely re-adsorbed in order to compensate for moisture released either from the stored goods or intruding into the container from the exterior, i.e. they scarcely act as desiccants. Thus, it is difficult to remove excess moisture from the atmosphere within a storage container. Furthermore, the surface of such moistened pads can represent a medium for the growth of microorganisms such as various bacteria, fungi, moulds, yeasts etc., the presence of which is usually not desirable, in particular when storing goods such as vegetables, flowers or tobacco products. In particular in the storage of goods that are intended for contact with human beings such as the aforementioned goods, the use of possibly hazardous agents for controlling proliferation of microorganisms is to be avoided.
Recently, it has been found that conventional desiccant materials, such as silica gel, molecular sieves and the like, can be hydrated to specific hydration levels. This means that water can be adsorbed to a level between the “dry” state (in which essentially no water has been adsorbed) and the saturation state (in which no further moisture is adsorbed from the environment). When these hydrated desiccant materials are placed within a sealed container or room, the relative humidity level of the environment within that container or room can be maintained at a higher predetermined relative humidity level.
Thus, the hydrated desiccant material can adsorb moisture from the surrounding atmosphere, when the relative humidity is higher than the desired level. Hence, in this case, the material acts as a desiccant. Furthermore, the hydrated desiccant material can also release moisture to the surrounding atmosphere, when the relative humidity is lower than the desired level. Hence, the hydrated humidity control substance can also act as humectant. In view of these properties, such hydrated desiccant materials are also referred to as humidity control substances.
In the context of the present application, the word “adsorb” is used in order to indicate that moisture is taken up from the surrounding atmosphere regardless of the underlying process. Any physisorption and chemisorption processes shall be included.
The conventional procedure used for hydrating desiccant products is to place those products in a constant humidity environment, such as a sealed room or oven, wherein the humidity of the environment surrounding the desiccant products to be hydrated is preset and maintained at the desired humidity level.
US 2006/0144733 A1 and US 2007/0228072 A1 describe containers for retaining moisture sensitive material. Said containers are provided with a humidity control-substance such as clay, silica gel and molecular sieve. In order to provide a humidity control substance having a moisture content sufficient for establishing and/or maintaining a desired humidity within said container, a humidity control substance having a moisture content lower than desired is hydrated by introducing the humidity control substance into a chamber providing an environment controlled with respect to humidity and allowing the humidity control substance to adsorb moisture from said environment.
In order to achieve the desired hydration levels, the desiccant products must be left in the constant humidity environment for a long period of time. Depending on the amount of desiccant to be treated and the desired level of hydration, this process can be quite slow and can take from several hours to several days. Furthermore, all of the desiccant products to be hydrated must be physically exposed to the humidity in the surrounding atmosphere in order to adsorb sufficient humidity such that the desired hydration level is achieved. This requires relatively thin layers of the desiccant product to be placed within the constant humidity environment and frequent mixing of the desiccant product so that the entire quantity of desiccant products can be hydrated. Otherwise, the moisture content of the hydrated desiccant product can be heterogeneous and the accuracy of the relative humidity established by the hydrated desiccant product can be insufficiently low. In addition, the relative humidity level within the room must be carefully monitored so that the desired hydration level of the desiccant products is achieved, regardless of the quantity of the desiccant products that are placed within that room. In addition, the energy costs associated with hydration of large quantities of humidity control substance using these sealed rooms can be substantial.
Accordingly, a process for the hydration of desiccant materials devoid of the above-mentioned disadvantages is desirable.
It is hence an object of the present invention to provide a process that allows the rapid and reliable preparation of hydrated humidity control substances and hence is suitable for the preparation of large quantities of hydrated humidity control substance in a time-efficient manner.